KIEV/DONETSK, Ukraine, April 18 (Reuters) - If armies march on their stomachs, then Ukraine's rival protest camps could be in for a long campaign, judging by the cooks hard at work behind the barricades in Kiev and Donetsk on Friday.

A day after Ukraine and Russia agreed that protest sit-ins must end, pro-Moscow separatists in eastern Ukraine said they would not quit occupied public buildings and pro-Western activists in the capital insisted they would not dismantle their Maidan camp, which helped topple the Kremlin-backed president.

"We're not going anywhere," said Ivana, a pensioner from the western city of Ternopil as she and half a dozen other women prepared soup and chopped salo - the national staple of salted lard. Their camp kitchen sits in the middle of Khreshchatyk, the elegant main boulevard of Kiev, barricaded since November.

"We've been here five months and we will stay until after the presidential election (on May 25), to see it's not rigged," she said as her party of cooks prepared to bake Easter cakes for activists to enjoy on Sunday morning.

In Donetsk, the coal and steel hub 700 km (400 miles) to the east near the Russian border, another pensioner, Alina, was also hard at work feeding men on the frontline of what has become the gravest face-off between Moscow and the West since the Cold War.

Making dozens of pungent sandwiches filled with tinned sardine in the occupied headquarters of the Donetsk regional government, Alina's goal is for her Russian-speaking, industrial region to cut its ties to Ukrainian-speakers like Ivana in the west and either stand alone or be annexed by Moscow. The protesters have declared the People's Republic of Donetsk.

"I came here a week ago to cook for my sons and daughters, since all them here are my children," said Alina. "I will stay here as long as they do. I hope they never surrender and that they will defend our Donetsk Republic."

Though among a relatively small hard core of impassioned partisans on either side, the cooks in Kiev and Donetsk, and the mirror-image paramilitary camps that have sprung up on opposing sides of the country pose a conundrum for the European monitors charged under the Geneva agreement with implementing a peace.

In Donetsk and close to a dozen other towns in the east, the lessons of the Maidan appear to have been learned. Similar walls of tyres, barbed wire, bric-a-brac and sandbags have sprung up.

As in Kiev, they could make it very hard for even determined and well trained security forces to swoop in without deploying the kind of lethal force that would risk provoking a backlash.

In Kiev two months ago, riot police ended up shooting dozens of demonstrators and within days the president fled to Russia. In the east, Ukrainian leaders fear bloodshed would give Moscow grounds to step in, as in Crimea, to "protect" Russian-speakers.

"Donetsk and Russia are one", "Down with the Kiev fascists" and "America, hands off Donetsk" are among banners hung around the entrance to the Soviet-era tower block now flying the flags of Russia, the Soviet Union and the local People's Republic.

MIRROR IMAGES

So far, Ukraine's security forces have said they are holding back for fear of "civilian" casualties. The most visible evidence of an "anti-terrorist operation" this week was the farcical capture of half a dozen armoured vehicles by gunmen in Slaviansk. Though Kiev said it killed three militants when a crowd tried to storm a military base in Mariupol to the south.

In lobbies, corridors and offices in Donetsk, dozens of activists, some with handguns, others with machetes, knives or clubs, keep themselves busy, operating a round-the-clock first aid post, canteen, public relations office and other services, including a non-stop soundtrack of patriotic wartime songs.

For many, the language and imagery recalls the drama of the people's soviets during the Bolshevik revolution of 1917.

The hectic energy mirrors that of Kiev's Independence Square, known locally as the Maidan, where people descended in their thousands in late November after President Viktor Yanukovich rejected closer ties with the European Union.

Though flush with victory since the overthrow of Yanukovich, the Maidan also retains its air of angry revolution, albeit today less crowded, less tense, and now jostling for space with the spread of pavement cafes and spring season deliveries to the fashionable stores lining Khreshchatyk.

The refusal of activists there to pack up their tents, or in the case of the hardline nationalists of Right Sector to give up the buildings they are operating from around the square, is also a stumbling block to a negotiated end to the occupations in the east, where leaders say they want the Maidan cleared first.

Ukraine's foreign minister said on Friday that the Geneva accord did not apply to the "legal" demonstration in Kiev, but Russia - which denies that it is orchestrating the protests in the east - was quick to say the Ukrainians had "misunderstood".

There are signs that the Kiev camp, under pressure from fatigue and the businesses around it, may be shrinking. The once occupied city hall on Khreshchatyk has been emptied of the anarchic paraphernalia of the uprising and painters are at work, paid for by civic-minded businesses, to repair the damage.

But just as in Donetsk, where machete-wielding Nikolai vowed to fight until the city becomes part of Russia, the groups on Kiev's central square and main shopping street remain ready for action, with barricades, rocks and petrol bombs on hand to repel any move by authorities of whatever party to sweep them aside.

Smiling broadly above the traditional peasant brocade of her blouse, her face tanned by a winter outdoors, the Maidan cook Ivana was missing home but not ready to leave: "Not till June, after the elections. And even then, only if they're not rigged." (Editing by Robin Pomeroy)

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